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Design stories: concept to reality

In 2013 Naim Audio has launched not only its first ‘desktop’ digital-to-analogue converter, the DAC-V1, but also a complete new line-up of NAIT amplifiers. Electronic Design Director Steve Sells and Senior Engineer Dave Barber tell Andrew Everard how digital and analogue development go hand in hand, and how computer modelling is making the design process both faster and more intriguing.

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In the past, every circuit change would involve building prototypes and testing them; now we can start by modelling all of this on the computer before we begin to build physical prototypes. We can explore how even the very smallest change affects the whole design, right through to the thermal effects of the location of components.”

Naim Audio Electronic Design Director Steve Sells is explaining the way the design process for Naim Audio’s new products has changed, and how those changes have influenced not just the DAC-V1 desktop digital-to-analogue converter, one of the company’s most popular new arrivals, but also that of the allnew NAIT range of integrated amplifiers. Sells points to the location of the output transistors in one of the amplifiers: “Using computer modelling, we could work out not just the best position for these components in sonic terms, but also to meet regulations on the maximum temperature for the product.

This doesn’t just speed up the design of products – it also allows much greater creativity and experimentation, in that many more ideas and ‘what ifs’ can be modelled and tested in the time previously taken to work up one prototype of a circuit or even a whole product.” As Naim Audio Senior Engineer Dave Barber puts it: “It allows us to run through many versions very quickly, try things – even the ones we’d probably never even have bothered with in the old ways. And it can throw up some real surprises and new avenues for exploration.”

Also, the two explain that it’s now much easier to carry over the technology from one product to something completely different, from the headphone amplifier in the DAC-V1 going into the new NAIT line, and the digital isolation techniques developed for the NDS finding their way into the DAC-V1, along with DAC technology from the NDX and SuperUniti.

"The final evaluation of a product’s performance always takes place in the listening room."

Dave Barber says that while the idea of designing a desktop DAC that accepts a direct connection from a computer was attractive, it posed a number of problems, notably the need to isolate the DAC circuitry from electrical noise from the computer or picked up on the connecting cable. To that end, the USB input makes no use of the power connection on the computer USB output, galvanic isolation is used to exclude noise completely, and bit-perfect test routines are built-in to make sure the DAC is getting what’s on the digital music files.

For all that, the engineers still found that different cable constructions, and indeed different lengths of USB cable, had audible effects on the sound during listening tests. Barber explains: “After all this computer modelling and analysis the final evaluation of a product’s performance always takes place in the listening room.”

In the new NAIT range – the NAIT 5si, NAIT XS 2 and SUPERNAIT 2 – the approach has been one of improving components and power supplies to improve sound quality and dynamic headroom, while also simplifying the layout of the products by reducing features. Most notable is the loss of the original SUPERNAIT’s digital inputs: Steve Sells explains, while this move apparently flies in the face of what others are doing, it was an easy decision.

The design team was determined to get maximum performance from the amplifier without increasing the price, and taking this “stripped down” approach enabled a significant gain while at the same time actually reducing the cost of the new amplifier. Or as Sells puts it: “It’s not easy to improve upon an icon. But by staying true to the stripped-back purest approach that won the original NAIT such a loyal following, I think we’ve managed to do just that.”

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